Have a friend go with you to the range and load your weapon one cartridge at a time. Sometimes your friend will load a live round. Other times your friend will load a dummy round (empty chamber or a once fired round or a "snap cap" round). This will help notice and correct the flinch.

The other suggestions are good. Increase trigger pull slowly until the firing pin drops unexpectedly. Dry firing is good practice. As far as breathing, what I have heard is take a deep breath, let out half of the breath, then shoot.

Good luck.